Gasoline fueled engines are typically designed so that under full load (open throttle) no uncontrolled combustion (knocking) occurs that limits the compression ratio. Under throttled conditions, the gasoline engine is under-compressed, which can reduce engine efficiency. Diesel fueled engines are typically over compressed to enhance starting in cold conditions. Diesel engines that have warmed up would be more efficient if they had a lower compression ratio. A need exists for an improved variable compression ratio engine and related methods.